Mercury Cadmium Telluride: Growth, Properties and Applications (Wiley Series in Materials for Electronic & Optoelectronic Applications)

Mercury Cadmium Telluride......Page 5
Contents......Page 9
Series Preface......Page 23
Preface......Page 25
Foreword......Page 29
List of Contributors......Page 33
Part One - Growth......Page 37
1.1 Introduction......Page 39
1.2 Phase equilibria......Page 40
1.3 Crystal growth......Page 41
1.3.1 Solid state recrystallization (SSR)......Page 42
1.3.2 Traveling heater method (THM)......Page 45
1.3.3 Bridgman......Page 48
1.3.4 Accelerated crucible rotation technique (ACRT)......Page 49
1.4 Conclusions......Page 54
References......Page 55
2.1 Introduction......Page 57
2.2.1 Cadmium......Page 58
2.3.1 Polycrystal growth......Page 59
2.3.2 VGF single-crystal growth......Page 60
2.4 Wafer processing......Page 77
2.4.1 Process flow......Page 78
2.4.2 Characteristics......Page 80
Acknowledgements......Page 84
References......Page 85
3 Properties of Cd(Zn)Te Relevant to Use as Substrates......Page 87
3.2.1 Ionicity......Page 88
3.2.2 Lattice constant and crystal density......Page 89
3.2.3 Spontaneous ordering......Page 90
3.3.1 Phase diagram......Page 91
3.3.2 Specific heat and Debye temperature......Page 92
3.3.4 Thermal conductivity and diffusivity......Page 93
3.4.2 Microhardness......Page 94
3.4.3 Optical phonon frequency and phonon deformation potential......Page 95
3.5.2 Fröhlich coupling constant......Page 97
3.6.1 Bandgap energy......Page 98
3.6.2 Electron and hole effective masses......Page 100
3.6.3 Electronic deformation potential......Page 101
3.6.4 Heterojunction band offset......Page 102
3.7.1 The reststrahlen region......Page 103
3.7.2 The interband transition region......Page 104
3.7.3 Near or below the fundamental absorption edge......Page 105
3.8.1 Low-field mobility......Page 106
References......Page 107
4 Substrates for the Epitaxial Growth of MCT......Page 111
4.1 Introduction......Page 112
4.2 Substrate orientation......Page 113
4.3.1 Effects of poor thermal conductivity on MCT growth......Page 114
4.3.2 Effects of substrate crystalline defects on MCT growth......Page 115
4.3.4 Effects of nonuniform substrate composition and substrate roughness......Page 116
4.3.6 Characterization and screening of CZT substrates......Page 117
4.4 Si-based substrates......Page 118
4.4.1 Nucleation and growth of CdTe on Si......Page 119
4.4.2 The effects of As and Te monolayers......Page 120
4.4.3 Advantages of CdTe/Si substrates......Page 121
4.4.4 Disadvantages of CdTe/Si substrates......Page 122
4.4.5 Reduction of the dislocation density......Page 123
4.4.6 Passivation of dislocations......Page 124
4.5 Other substrates......Page 125
References......Page 126
5.1 Introduction......Page 131
5.2.1 Introduction......Page 132
5.2.3 LPE growth techniques......Page 134
5.3.1 Composition and thickness......Page 139
5.3.2 Crystal quality and surface morphology......Page 141
5.3.3 Impurity doping and electrical properties......Page 142
5.5 Summary and future developments......Page 144
References......Page 146
6.1 Requirement for epitaxy......Page 149
6.2 History......Page 150
6.3.1 Orientation......Page 151
6.3.2 Material......Page 152
6.4 Reactor design......Page 153
6.5 Process parameters......Page 154
6.6 Metal-organic sources......Page 155
6.8 Reproducibility......Page 156
6.9 Doping......Page 159
6.10 Defects......Page 161
6.12 In situ monitoring......Page 163
References......Page 164
7.1 Introduction......Page 167
7.2 MBE Growth theory and growth modes......Page 168
7.2.2 Quasiequilibrium theories......Page 169
7.2.3 Kinetic theories......Page 170
7.4.1 Reflection high-energy electron diffraction......Page 171
7.4.2 Spectroscopic ellipsometry......Page 172
7.5 MCT nucleation and growth......Page 175
7.6 Dopants and dopant activation......Page 177
7.7.1 Electrical properties......Page 179
7.7.3 Structural properties......Page 180
7.7.4 Surface defects......Page 181
7.8 Conclusions......Page 182
References......Page 183
Part Two - Properties......Page 187
8 Mechanical and Thermal Properties......Page 189
8.1.2 Variation of density with x......Page 190
8.1.3 Variation of density with temperature......Page 191
8.2.2 Variation of lattice parameter with x......Page 194
8.2.3 Variation with temperature......Page 196
8.3.2 Variation with x......Page 198
8.3.3 Variation with temperature......Page 199
8.4.1 Introduction......Page 202
8.4.2 Elastic parameter values......Page 203
8.5.2 Hardness......Page 206
8.5.3 Deformation characteristics of MCT......Page 210
8.5.5 Conclusion......Page 216
8.6.3 Solid phases......Page 217
8.6.4 Quasibinary systems......Page 219
8.6.5 Liquidus, solidus, and solvus surfaces......Page 221
8.6.6 Thermodynamics......Page 222
8.7.2 Temperature variation of kinematic viscosity of the MCT melt......Page 223
8.8.2 Specific heat (Cp)......Page 225
8.8.3 Thermal diffusivity (Dθ)......Page 228
8.8.4 Thermal conductivity (Kθ)......Page 230
References......Page 233
9.1 Introduction......Page 241
9.3 Theory of band to band optical transition......Page 242
9.4 Near band gap absorption......Page 243
9.5 Analytic expressions and empirical formulas for intrinsic absorption and Urbach tail......Page 245
9.6 Dispersion of the refractive index......Page 252
9.7 Optical constants and related van Hover singularities above the energy gap......Page 253
9.8 Reflection spectra and dielectric function......Page 256
9.9 Multimode model of lattice vibration......Page 257
9.10 Phonon absorption......Page 258
9.11 Raman scattering......Page 261
9.12 Photoluminescence spectroscopy......Page 263
References......Page 267
10.1 Introduction......Page 275
10.2 Self-diffusion......Page 276
10.2.3 Te self-diffusion......Page 277
10.2.5 Conclusions......Page 278
10.3.1 Composition: xCd ~ 0.2......Page 279
10.3.3 Cadmium telluride (CdTe)......Page 281
10.3.4 Conclusions......Page 282
10.4 Compositional interdiffusion......Page 283
10.4.1 D from CID profiles of xCd versus x......Page 284
10.4.2 Conclusions......Page 288
10.5 Impurity diffusion......Page 289
10.5.1 Group 1 impurities......Page 290
10.5.2 Group 3 and 5 impurities......Page 292
10.5.3 Group 6 and 7 impurities......Page 294
References......Page 296
11.1 Introduction......Page 299
11.2 Native point defects in zincblende semiconductor......Page 300
11.3 Measurement of native defect properties and density......Page 302
11.4.1 Defect formation energies......Page 304
11.4.2 Electronic excitation energies......Page 305
11.4.4 Prediction of native point defect densities in HgCdgTe......Page 306
References......Page 308
12.1 Introduction......Page 311
12.2.2 Valence band offset......Page 313
12.3.1 k·p theory......Page 315
12.3.2 Hybrid pseudopotential tight-binding method......Page 317
12.4.1 Optical absorption......Page 324
12.4.2 Auger recombination......Page 325
References......Page 329
13.1 Introduction......Page 333
13.2 Native defects in undoped MCT......Page 334
13.3 Native defects in doped MCT......Page 337
13.4 Defect concentrations during cool down......Page 338
13.5.1 CTC by thermal annealing......Page 340
13.6.1 IBM of vacancy-doped MCT......Page 343
13.6.2 Modeling of IBM......Page 345
13.6.4 Stability (relaxation) of CTC layers with respect to time and temperature after IBM......Page 347
13.7.2 CTC with H2/CH4 plasmas......Page 349
13.8 Summary......Page 350
References......Page 351
14 Extrinsic Doping......Page 353
14.1 Introduction......Page 354
14.2 Impurity activity......Page 355
14.2.2 Group II impurities......Page 356
14.2.6 Group VI impurities......Page 357
14.3.1 CdTe......Page 358
14.3.2 LWIR and MWIR MCT......Page 359
14.4 Segregation properties of impurities......Page 360
14.4.1 Segregation in CdTe......Page 361
14.4.2 Segregation in LWIR and MWIR MCT......Page 362
14.5 Traps and recombination centers......Page 363
14.5.2 Reducing the concentrations of SRH centers......Page 364
14.6.1 In......Page 366
14.6.2 Iodine......Page 367
14.6.4 As......Page 368
14.7 Residual defects......Page 370
References......Page 371
15 Structure and Electrical Characteristics of Metal/MCT Interfaces......Page 375
15.1 Introduction......Page 376
15.2.2 In/MCT interface......Page 377
15.2.3 Ag/MCT interface......Page 378
15.2.6 Cr/MCT interface......Page 379
15.3.1 Al/MCT interface......Page 380
15.3.4 Ti/MCT interface......Page 381
15.3.6 Sn/MCT interface......Page 382
15.4.2 Device design and passivation requirements......Page 383
15.4.5 Passivation of MCT with CdTe......Page 384
15.5.2 Metal/MCT contacts......Page 390
15.5.3 Schottky barrier contacts......Page 391
15.6.1 Introduction......Page 392
15.6.3 Recombination velocity at heterointerfaces......Page 393
15.6.5 Gated photodiodes......Page 394
15.7.1 Introduction......Page 395
15.7.2 Surface structure and epitaxial growth......Page 396
15.7.3 RHEED analysis of the (211) surface......Page 397
15.7.4 Reconstruction of the (110) surface......Page 399
15.7.5 Reconstruction of the (100) surface......Page 401
15.7.6 Reconstruction of (111) surfaces......Page 403
References......Page 406
16 MCT Superlattices for VLWIR Detectors and Focal Plane Arrays......Page 411
16.1 Introduction......Page 412
16.2 Why HgTe-based superlattices......Page 413
16.2.1 Advantages of HgTe/CdTe superlattices over MCT alloys......Page 414
16.2.2 Problems with the use of HgTe/CdTe superlattices in VLWIR detectors and FPAs......Page 417
16.2.3 Use of HgTe/CdTe superlattices as buffer layers on CdZnTe before MCT growth......Page 418
16.2.5 HgTe/ZnTe superlattices......Page 419
16.3.1 Normal electronic band structure: band structures and optical absorptivities......Page 420
16.3.2 Inverted electronic band structure: band structure and optical absorptivity......Page 421
16.4 Growth......Page 422
16.4.1 Substrate orientation......Page 423
16.4.2 Doping......Page 424
16.5 Interdiffusion......Page 425
16.5.1 Effect of interdiffusion on the bandgap and optical absorption spectra......Page 426
16.5.2 Measuring interdiffusion by X-ray diffraction......Page 427
16.5.3 Measuring interdiffusion by STEM......Page 429
16.6 Conclusions......Page 431
References......Page 432
17 Dry Plasma Processing of Mercury Cadmium Telluride and Related II–VIs......Page 435
17.1 Introduction......Page 436
17.2 Effects of plasma gases on MCT......Page 437
17.3.1 Physics of plasmas......Page 439
17.3.2 Hydrogen variations......Page 441
17.3.3 Plasma parameters – effects on II–VI semiconductors......Page 444
17.3.4 Plasma parameter change ECR to ICP......Page 446
17.4.1 Surface chemical analysis......Page 447
17.4.3 Ex vacuo atomic force microscopy......Page 449
17.5.1 Etch lag and lateral photoresist etching – ion angular distribution (microloading, RIE lag)......Page 452
17.5.2 Macroloading......Page 454
17.6 Plasma processes in the production of II–VI materials......Page 456
17.6.1 Trench delineation......Page 457
17.6.4 Microlenses and antireflective structures......Page 458
17.7 Conclusions and future efforts......Page 460
References......Page 461
18.1 Introduction......Page 465
18.1.1 Historical perspective and early detectors......Page 466
18.1.3 MCT photoconductive arrays......Page 467
18.2 Applications and sensor design......Page 468
18.3 Photoconductive detectors in MCT and related alloys......Page 470
18.3.1 Introduction to the technology of photoconductor arrays......Page 471
18.3.2 Theoretical fundamentals for LW arrays......Page 472
18.3.4 Nonequilibrium effects in photoconductors......Page 475
18.4.1 Introduction to the SPRITE detector......Page 476
18.4.2 SPRITE operation and performance......Page 477
18.5 Conclusions on photoconductive MCT detectors......Page 480
References......Page 481
Part Three - Applications......Page 483
19 HgCdTe Photovoltaic Infrared Detectors......Page 485
19.3 Applications......Page 486
19.4.1 Ideal photovoltaic devices......Page 487
19.4.2 Nonideal behavior in MCT diodes......Page 488
19.5.1 Thermal diffusion currents in MCT......Page 490
19.5.3 Interband tunnelling......Page 491
19.5.5 Impact ionization......Page 492
19.6 Manufacturing technology for MCT arrays......Page 493
19.6.2 Via-hole technologies using LPE......Page 494
19.6.3 Planar device structures using LPE......Page 495
19.6.4 Double layer heterojunction devices (DLHJ)......Page 496
19.6.5 Wafer-scale processes using vapor phase epitaxy on low-cost substrates......Page 497
19.7.1 Two-color array technology......Page 499
19.7.2 Higher operating temperature (HOT) device structures......Page 500
References......Page 501
20.1 Introduction......Page 505
20.2.1 Introduction and theory......Page 506
20.2.2 Nonequilibrium detectors......Page 509
20.3.1 Introduction......Page 512
20.3.2 Mesa diodes......Page 513
20.3.3 Planar diodes......Page 518
20.3.4 Stacked loophole......Page 519
20.4 Emission devices......Page 520
References......Page 525
21.1 Introduction and applications......Page 529
21.2 The avalanche multiplication effect......Page 530
21.3 Physics of MCT EAPDs......Page 531
21.3.1 Phenomenological model for EAPDs......Page 532
21.3.2 Energy dispersion factor, α(E)......Page 533
21.3.3 Impact ionization threshold energy......Page 535
21.3.4 EAPD diodes at room temperature......Page 537
21.3.5 MCT EAPD dark currents......Page 539
21.4.1 Theoretical foundations for the EAPD device technology......Page 540
21.4.2 Via-hole technology......Page 541
21.5.1 Avalanche gain......Page 542
21.5.3 Dark current......Page 543
21.6 LGI as a practical example of MCT EAPDs......Page 546
References......Page 547
22.1 Introduction......Page 549
22.2.1 Generalized model......Page 550
22.2.2 Reduced volume devices......Page 553
22.2.3 Design of high temperature photodetectors......Page 554
22.3.1 Ultimate performance of HgCdTe devices......Page 555
22.3.2 Non-equilibrium devices......Page 557
22.4 Photoconductive devices......Page 558
22.5.1 PEM detectors......Page 560
22.5.2 Magnetoconcentration detectors......Page 561
22.6 Photodiodes......Page 562
22.6.2 Practical HgCdTe photodiodes......Page 563
References......Page 571
Index......Page 575